Sometime near 2007-11-11 00:15 -0500, Marcio Marchini shouted:
Researching online one can see that WebDAV's spec requires that they check both src and dest URLs for protocol & port. But with some proxies or SSL fronts like stunnel, only one of the URLs is rewritten, so one goes as http and the other as https. Here's one person explaining it, much better than me: http://svn.haxx.se/users/archive-2006-03/0549.shtml
Stunnel doesn't currently have the ability to scan and re-write the plaintext. For HTTP redirects it could possibly be implemented (re-write only the response before ^$, and redirects aren't chunked and don't have content lengths to work with, etc) but you'd still need enough HTTP logic to handle keepalives and such. It's not trivial and not likely.
Another option would be to have something already HTTP aware doing the rewriting in between stunnel and subversion. A re-writing proxy.
Another option would be to use mod_rewrite in apache to rewrite the urls.
But the best way would be to just use SSL inside apache and drop stunnel entirely.